Crack Growth Model of Pipeline Steels in Near-Neutral pH Soil Environments

This paper reports the crack growth behavior of pipeline steels in near-neutral pH environments. Crack growth data both from laboratory tests using compact tension (CT) specimen and from full scale tests of shallow cracks were analyzed using a true corrosion-fatigue model established recently. It has been found that the crack growth rate can be correlated with ΔK²K_max/f^α, where ΔK is the stress intensity factor range; K_max is the maximum stress intensity factor; f is the loading frequency; and α is a factor related to corrosivity of soil environments. This correlation enables determination of threshold ΔK²K_max/f^α values for long cracks such as in a test using CT specimen. The above growth correlation appears also true for small/shallow cracks in full scale tests except that small/shallow cracks were found to grow at appreciable rates below the threshold of long/deep cracks. Implications of the growth model to crack growth occurring in the field and pipe integrity management were also discussed in the paper.